Method of smelting tin-containing materials



Patented Aug. 8, 1944 METHOD or SMELTINGTlN-CONTAINING MATERIALS 7 Louis s. Deitz, Jr., Westfleld, N. 1., assignor to" Nassau Smelting & Refining Company-,lncorporated, New York, N. Y., a corporation of New York Application August 20, 1942 Serial No. 455.439

' 21 Claims.

This invention relatesto methods of smelting tin-containing materials and more particularly to methods of electrically smelting tin-containing materials in a slag resistance furnace.

An electric slag resistance furnace operates on the principle of heat generated by means of the electrical resistance oifered to the passage of current in a molten slag conductor. In operation, the slag is meltedfirst and the charge is fed into the top of thefurnace and rests on top of the slag, which is maintained at any temperature desired by varying the amount of current passing therethrough. As the charge is smelted, the metal being heaviensinks through the slag to the bottom of the hearth from whichpoint it may be tapped out directly into molds.

The resistance of certain of the slag resistance furnaces heretofore employed to smelt metallic materials has been controlled either by varying the depth of the slag layer, or the distance between the electrodes, or the temperature of the slag layer. None of these various methods of controlling the resistance of the furnace eliminates arcing in the furnace and the consequent vaporizing of considerable quantities of metal.

An object of this invention is to provide new and improved methods of and slags for smelting tin-containing materials.

A method of smelting tin-containing materials in a slag resistance furnace which embodies the present invention comprises maintaining the resistance in such a furnace between predetermined values by adding to the slag in the furnace a material which has the property of varying the conductivity of the slag.

Other features and advantages of the invention will become apparent from the following detailed description of one embodiment thereof, when read in conjunction with the accompanying drawing, in which the single figure is a vertical sectional view of an electric slag resistance furnace.

Theparticular furnace disclosed in the accompanying drawing comprises a cylindrical furnace body In having a chamber H formed therein. The furnace body may be constructed of any suitable refractory material retained within a steel shell (not shownlas is well known in the construction of this type of furnace and is provided with a cover l2 in which a feed hole I4, a flue l5, and a centrally located,

opening l6 are formed. The cover I2 is made of refractory material ofthe type which is generally used for similar purposes and which is wellknown to those skilled in this art. While I only one feed hole i4 is shown, the number of and the location'fof feed holes in the cover l2 may bevaried to suit individual requirements.

A vertically movable electrode I8 extends through the opening IS in the cover II and is supported at its uppermost end by a water-cooled clamp 19. The clamp l9 isflxedly connected to a channel bar 20 in which a groove 2| is formed.

.The groove 2| receives rollers 22-42 which are rotatably mounted upon a support member 23, so as to guide the channel bar 20 during its vertical' movements. The lowering and raising of the electrode [8 through the operation of the the operator causes the worm-gear 24 to rotate by turning a hand wheel 29.

A block 30 of conducting material, such as graphite, is disposed centrally at the bottom of thechamber ll so that the top of the block 30 is approximately even with the bottom of the chamber II. A water cooled electrode holder 4| is clamped to a graphite electrode 3| which connects the block 30 to a source 32 of electric ity, while the electrode l8is connected to an oppositely charged source 34 of electricity. The block 30 may be omitted so that the graphite electrode! provides the electrode contact within the furnace through the molten metal 38.

The accompanyingdrawing shows a typical condition of the materials within the furnace H).

An upper layer 35 within the chamber H rep-- resents charge materials, an intermediate layer 36 represents molten slag, and a lower layer 38 represents molten metal. The layer 35 of charge materials is lighter than either the molten slag layer 36 or the molten metal layer 38, and, therefore, floats on the top of the other materials. The molten metal38 being the heaviest rests upon the bottom ofthe chamber ll. When the charge has become heated sufliciently to bring about a chemical reduction of the metallic compounds to metal, the metal is gradually fiuxed out of the charge and gravitates through the slag layer 36 to the metal layer 38 upon the bottom of the chamber l l. The metallic compounds which are not reduced by this process, along with otherimpurities, gradually accumulate in the slag layer 36 which is tapped off from time to time through an opening 39. An opening 40, which is level with the bottom of the chamber II, is provided for tapping off the molten metal in the layer 38.

One method of operating a 114 kva. furnae of the type described herein-above, which has been found satisfactory for this purpose, will now be described in detail. Water is started running through the water-cooled electrode holders I 9 and 4| and a small mound of crushed coke is placed on the bottom electrode block 30. The movable electrode I8 is lowered until the tip of it touches the coke, and the: electrodes 18 and 30 are then connected to a source of electrical power. A potential of from about 30 to about 55 volts may be impressed upon the electrodes, 48 volts having proved satisfactor in actual practice. The circuit is adjusted by varying the position of the electrode l9 until a current of about 1000 amperes fiows through the furnace.

A slag mix consisting of about 87 pounds of sand,

about 100 pounds of limestone, and about 65 pounds of sodium carbonate is fed into the chamber l| throughthe feeding hole H at the rate of 6 shovels every five minutes. When all this slag mix has been fed into the chamber II, the amperage 'is raised to about 1500 amperes, and about 500 pounds of old slag in a divided form is added. When the slag is completely molten, the amperage is raised to about 2700 amperes, and some of the charge is then fed through the feed hole I4 into the chamber ll. 7

An illustrative charge suitable for producing a tin-lead alloy may be as follows:

nance cost thereof. The resistance of the slag is so regulated that the over-all resistance of the furnace, which in this particular example has an inside diameter of approximately 40 inches, is between about .010 ohm and about .025 ohm when the slag depth is between 6 to 12 inches and the furnace is operating at 48 volts and 2700 ampres. The resistance of the slag is decreased by sodium carbonate additions, and the sodium carbonate content of the slag is regulated by controlling the amount thereof in the charge. Since the charge is constantly being renewed, it is evident that the resistance of the slag may be readily maintained within predetermined limits by periodically adjusting the sodium carbonate content of the charge. Under these conditions of operation, the current passing through the furnace is steady and there is no arcing between the electrodes. Consequently, little or no tin is lost through fuming or volatilization.

The chargeis fed into the furnace at short.

intervals and sufficient charge is supplied to maintain a layer thereof on top of the molten slag. This layer of charge should be thick enough to prevent loss of metal through fuming and to permit preheating of the charge, but not so thick that the charge tends to cake or to sink into the slag. A layer of from three to eight inches thick has been found to give satisfactory results in a furnace of the type in question. a

A total amount of material equal to two charges such as that described above is gradually fed into the furnace through the feed hole I! every twenty-four hours. The molten slag is removed once very twenty-four hours through the slag tap 39, while the molten metal is removed once every eight hours through the metal tap 40. Approximately 1,300 to 1,400 pounds of metal is removed each time the pot II is tapped, so that the furnace has a daily production of approximately 4,000 pounds. The metal produced is a lead-tin solder containing from about 42% to about 44% of tin. The slag removed Sn Weight Pounds Per cent Per cent Pounds Percent Tin cgnoentrates Tin cable sheath Total tin and lead.

Limestone Charcoal LI: Coal; dust Hi0} (in concentrates).

The ratio of tin to iron in the charge should be maintained between about 7 to 1 and about 12' to l, in order to prevent formation of iron-tin alloys, and preferably, this ratio should be about 8 to l. The ingredients in the charge are such as to maintain a slag which, excluding the various impurities, contains the equivalent of about 23% C210, about 18% FeO, about 36% S102 and about 10% NazO.

The temperature of the molten slag within the furnace is preferably kept below 2300 F., in order to reduce to a minimum the loss of tin through volatilization. A temperature of from about 2100 F. to 2300 F. has been proved to be satisfactory. In addition, the maintenanceof a low operating temperature greatly increases the life of the furnace and decreases the mainte- 55% or more of tin, while the slag tapped from the furnace usually will contain less than 2% of tin. The slag may be included in a blast furnace charge to recover the tin therefrom if the tin content of the slag is sufficiently high to justify further treatment. By using concentrates and drosses that are practically free from lead, substantially pure tin may be produced.

The following specific example illustrates a particular method embodying the present invention for smelting tin ores and drosses to produce relatively pure tin. In accordance with this of the slag within the desired li'mits.

. slag between predetermined values.

method a 275 kva. furnace is used and a typical charge may be as follows:

furnace likewise may be employed either alone or in combination with the carbonates. While Percent Pounds Percent Fe Sb Pound Pounds Percent Pounds Percent Pounds Percent Pounds Sn Sn Fe Sb Pb Pb Cu Cu Bolivian conc 1, 300 74. 2 970 1.72 22 .08 1.0 ll 1.4 .03 .4 Mexican conc r 200 44.28 89 13.93 28 .91- 1.8 .09 .2 .03 Mixed tin drosses 1,300 46.0 600 5.0 65 .40 5. 2 9 12.0 .8 10.0 Limestone 130 Soda Aah so and 140 Charcoal 60 Goal dust 200 The slags analyze aproximately 14% CaO, 15%

R0, $102, 8% NazO, balance ZnO, AlzOa,'

etc.

As in the previous example, the charge contains sodium carbonate as a slag resistance-controlling material. The amo'unt thereof in the charge is controlled to-maintain the resistance The product of this smelting operation is a pig tin containing about 97% of tin. I

This invention presents several distinct advantages over other well known methods ofsmelting similar tin-containing material. In the process of the present invention the smelting operatlon is continuous, except for a two hour discontinuance of feeding the charge once every twenty-four hours, as opposed to the intermittent smelting in a reverberatory furnace. The lower temperatures at which the above-described furnace-operates and the freedom of products of combustion for heating the charge decreases the amount of gas given off during the operation of the furnace and reduces to a minimum the loss of tin through vaporization. Lower operating temperatures also permit a lower maintenance cost as respects refractory linings and flues and greatly increases the life of the furnace.

When a sufficient amount of sodium carbonate is added to the slag within the furnace to increasethe conductivity thereof to a point where no arc can form between the electrodes, the electric current passes through the furnace in a steady flow. As a result, the furnace operates more economically, both with respect to the amount of current used and the amount of tin lost through fuming due to arcing. The small amount of fume produced may be readily collected and recovered by methods known to the art. The only tin lost isthat which remains in the molten slag. The slag generally contains only from about 2% to about 4% of tin, and in most cases less than 2% of tin. The tin content of the molten metal may be such that for many purposes, such as for copper base alloys, it need not be rerun to increase the amount of tin therein. Many other advantages are embodied in this invention and will be apparent to those skilled in the art.

Numerous modifications may be made inthe particular embodiments of the invention above described without departing from the spirit of the invention. The charge that is fed into the furnace may contain tin drosses, tin ores, lead drosses, solder dresses and other oxidized tin and lead products from which tin, lead and/or tinlead alloys, such as solder, may be recovered. Potassium carbonate may be substituted for sodium carbonate to maintain the resistance of the Also. salts of potassium and sodium, other than the carbonates, whiclihave no deleterious effect upon the metallic elements or other materials within the potassium salts may be used, the cheaper sodium salts are preferably employed for the sake of economy. The sodium carbonate content of the slag, calculated as NazO, may vary from about 5% to about 15%, although from about 8% to about 12% NazO has been found to give good results in actual practice. The other ingredients of the slag are adjusted to give the desiredfluidity and slagging effect for the particular materials being smelted.

What is claimed is: i

l. The method of smelting tin-containing material in an electric slag resistance furnace, which comprises maintaining the electrical resistance of the slag in such a furnace within predetermined limits by making controlled additions of sodium carbonate'thereto as the smelting operation progresses.

2. The methodof smelting tin-containing material in a slag resistance furnace, which comprises gradually adding to the slag in such a furnace material of the group consisting of sodium carbonate and potassium carbonate in such quantity as to maintain the electrical resistance of the slag between predetermined values.

3. The-method of smelting tin-containing material in an electric slag resistance furnace, which comprises maintaining the electrical resistance of the furnace at a predetermined value by gradually adding sodium carbonate to the slag within the furnace, and maintaining the temperature of the slag at a value not exceeding about 2300 F'.

4. The method of smelting tin-containing materials in a slag resistance furnace, which comprises gradually feeding into such a furnace a charge comprising tin-containing material, reducing material, slagging material and sodium carbonate, and regulating the sodium carbonate content of the charge'so as to maintain the electrical resistance of the slag produced in the furnace within predetermined limits.

5. The method of smelting tin-containing material in an electric slag resistance furnace, which comprises maintaining the electrical resistance of such a furnace between predeterminedvalues by gradually adding predetermined qualities of sodium carbonate to the slag within the furnace as the smelting progresses, and proportioning the constituents of the charge that is fed into the furnace so that the ratio of the tin to any iron in the charge is in excess of 7 to 1.

6. The method of smelting tin-containing materials in a slag resistance furnace, which comprises gradually feeding into such a furnace limits, and maintaining the temperature of the slag at a value not exceeding about 2300 F.

'7. The method of smelting tin-containing materials in a slag resistance furnace, which comprises gradually feeding into such a furnace a charge comprising tin-containing material. carbonaceous reducing material, slagging material and an alkali carbonate and in which the ratio of the tin in the charge to any iron therein is at least 7 to 1, and maintaining the electrical resistance of the slag produced in the furnace within predetermined limits principally by regulating the alkali carbonate content of the charge.

8. The method of smelting tin-containing materials in a slag resistance furnace, which comprises gradually feeding into such a furnace a charge comprising tin-containing material contaminated with iron, carbonaceous reducing material, sand, limestone and sodium carbonate, the ratio of the tin to the iron in the charge being at least 7 to l, maintaining the electrical resistance of the slag produced in the furnace within predetermined limits by regulating only the sodium carbonate content of the charge, and maintaining the temperature of the slag below 2300 F.

9. The method of smelting tin-containing material in a slag resistance furnace, which comprises gradually adding sodium carbonate to the slag in such a furnace in such quantities as to maintain the electrical resistance of the slag substantially constant, and maintaining the temperature of the slag between about 2100 F. and about 2300" F.

10. The method of. smelting tin-containing materials in a slag resistance furnace, which comprises successively feeding into such a furnace a plurality of charges comprising tin-containing material, reducing material and fluxing materials in substantially constant proportions, causing sodium carbonate to be present in each of the charges, and regulating the sodium carbonate content of the respective charges as the smelting operation proceeds so as to maintain the electrical resistance of the resulting slag layer within predetermined limits.

11. The method of smelting tin-containing materials in a slag resistance furnace, which comprises successively feeding into such a furnace a plurality of charges comprising tin-containing material. carbonaceous reducing material, sand and limestone in substantially constant proportions, causing sodium carbonate to be present in each of the charges, and regulating the sodium carbonate content of the respective charges as the smelting operation proceeds so as to maintain the electrical resistance of the resulting slag layer substantially constant.

12. The method of smelting tin-containing materials in a slag resistance furnace, which comprises successively feeding into such a furnace a plurality of charges comprising tin-conta ning material, carbonaceos reducing material. sand and l mestone in substantially constant proportions. causing sodium carbonate to be present in each of the charges, regulating the sodium carbonate content of the respective charges as the smelting operation proceeds so as to maintain the electrical resistance of the re sulting slag layer substantially constant, and maintain ng the temperature of the slag layer at a value not exceeding about 2300 F.

13. The method of smelting tin-containing materials in a slag resistance furnace, which substantially constant,

to maintain the electrical resistance of the re-- sulting slag layer substantially constant.

14. The method of smelting tin-containing materials in a slag resistance furnace, which comprises successively feeding into such a furnace a plurality of charges comprising tin-containing material, reducing material and fiuxing materialsin substantially constant proportions, causing suflicient'sodium carbonate to be present ineach charge to lower appreciably the electrical resistance of the resulting slag, and regulating the sodium carbonate content of the respective charges as the smelting operation proceeds so as to maintain the electrical resistance of the resulting slag layer substantially constant.

15. The method of smelting tin-containing materials in a slag resistance furnace, which comprises successively feeding into such a furnace a plurality of charges comprising tin-containing material, carbonaceous reducing material, sand and limestone in substantially constant proportions; including suflicient sodium carbonate in each charge to maintain a slag containing the equivalent of about 10% of NazO, regulating the sodium carbonate content of the respective charges as the smelting operation proceeds so as to maintain the electrical resistance of the resulting slag layer substantially constant, and maintaining the temperature of the slag layer between about 2100 F. and about 2300 F.

16..' Ihe method of smelting tin-containing materials in a slag resistance furnace, which comprises successively feeding into such a furnace a plurality of charges comprising tin-containing material, carbonaceous reducing mate-- rial, sand and limestone in substantially constant proportions, causing suflicient Sodium carbonate to be present in each charge to lower materially the electrical resistance of the resulting slag, regulating the sodium carbonate content of the respective charges as the smelting operation proceeds so as to maintain the electrical resistance of the resulting slag layer and maintaining the temperature of the slag layer between about 2100 F. and about 2300 F.

1'7. The method of smelting tin oxide materials in a slag resistance furnace, which comprises gradually feeding into such a furnace a charge comprising tin oxide ore and other tin oxide material, carbonaceous reducing material, sand and limestone in substantially constant proportions, causing sufflcient sodium carbonate to be present in the entire charge to lower materially the electrical resistance of the resulting slag, and regulating the sodium carbonate content of the charge as the smelting operation proceeds so as to maintain the electrical resistance of the resulting slag layer within predetermined limits.

18. The method of smelting tin oxide materials in a slag resistance furnace, which comprises gradually feeding into such a furnace a charge comprising tin oxide material, carbonaceous reducing material, sand and limestone in substantially constant proportions, causing suffia cient sodium carbonate to be present in the entire charge to lower materially the electrical resistance of the resulting slag, regulating the sodium carbonate content of the charge as the smelting operation proceeds so as to maintain the electrical resistance of the resulting slag layer substantially constant, and maintaining the temperature of the slag layer below 2300 F.

19. The method of producing solder in a slag resistance furnace, which comprises gradually feeding upon the molten slag layer in such a furnace a charge consisting essentially of tin ore and other tin-containing material, lead-containing material, reducing material, slagging material and sodium carbonate, so regulating the sodium carbonate content of the charge as the operation proceedsas to maintain the electrical resistance of the resulting slag layer within predetermined limits, and maintaining the tem perature ofthe slag layer at a value not exceeding about 2300 F. I

20. The method of producing pig. tin in a slag resistance furnace, which comprises gradually feeding upon themolten slag layer in such a furnace a charge consisting essentially of tin ore and other tin-containing material, reducing material, slagging material and sodium carbonate, so regulating the sodium carbonate content of the charge as the operation proceeds as to maintain the electrical resistance of the resultingslag layer within predetermined limits, and maintaining the temperature of the slag layer at a value not exceeding about2300 F.

21. The method of smelting tin-containing materials in a ,slag resistance furnace, which comprises gradually feeding upon the slag layer in such a furnace a charge comprising tin ore and other tin-containing material, carbonaceous reducing material, fiuxing material and sodiumcarbonate, the amount of sodium carbonate in the charge being sufficient to maintain the equivalent ofapproximately 5% to 15% of Na2O in the slag layer and any iron present in the charge being not more than about oneseventh of the tin content thereof, so varying the sodium carbonate content of the charge .as the smelting-operation progresses as to maintain the electrical resistance of the slag layer within predetermined limits, and maintaining thetemperature of the slag layer below about LOUIS S. DEITZ, JR. 

